1. Field of the Invention:
The present invention relates to a method for forming a surface layer of a carbide or nitride of a metallic element, such as vanadium, niobium, and chromium, or boron nitride on the surface of ceramics, such as silicon nitride (Si.sub.3 N.sub.4) and silicon carbide (SiC).
2. Related Art Statement:
Nowadays, specialty ceramics, such as silicon nitride and silicon carbide, are attracting public attention because of their outstanding physical properties and functions. Despite their high strength and high heat resistance, they lack toughness and they still have much room for improvement in mechanical properties, such as frictional properties and thermal impact resistance.
Ceramics are required to have more functions if they are to find use as electronic parts. Further, ceramic are expected to be a structural material, but there is a limit to increasing the density of ceramics products because they are made by sintering. So, it has been desired to produce denser ceramics with improved mechanical and physical properties.
There has been proposed to overcome the above-mentioned disadvantages of ceramics the modification of ceramic surfaces or the coating of ceramic surfaces with ceramic of similar or dissimilar kind. Related arts include Japanese Patent Publication Nos. 153757/1979 and 145088/1982 for extending tool life by the coating of ceramic surfaces with a metal nitride, carbide, or oxide; Japanese Patent Publication No. 71581/1985 for improving lubrication properties at high temperatures by the coating of ceramic surfaces with ceramics; and Japanese Patent Publication No. 29463/1985 covering the coating of ceramic surfaces with superconducting NbN. According to these related arts, the coating of ceramics is accomplished by the PVD process (physical vapor phase deposition), CVD process (chemical vapor phase deposition), or plasma jet process. These processes require a large-scale apparatus and much labor, and they do not form a uniform coating depending on the shape of an article to be treated.